The invention relates to a method and an arrangement for the automatic determination of an exposure value by means of electrical signals obtained from integrated and selective brightness measurement of the object to be exposed, for the exposure control in photographic cameras.
In general, the exposure metering in photographic cameras can be classified, according to the sensitivity characteristic towards the incident light, as integrated exposure metering, center-weighted exposure metering (or integrated metering with weighting of the central region) and as spot exposure metering. These types of exposure metering are advantageous in one respect and have disadvantages in others. Particularly when photographing a person in backlighting, for example, before a background of the sea or a snow-covered mountain, the main subject, namely the person, is greatly underexposed when integrated exposure metering or center-weighted exposure metering is used. In contrast, the exposure is essentially correct for such a photograph when spot exposure metering is used, but peripheral objects, which represent the background, are strongly overexposed. In each case, a photograph is obtained which is poorly balanced. To counteract this, Japanese Patent Application No. 26,229/1978 discloses that light values can be determined using spot exposure metering and integrated exposure metering with weighting of the picture center, a mean, which serves for exposure control, being derived if the difference between the two exceeds a pre-determined value.
In addition, German Offenlegungsschrift No. 2,838,227 discloses an exposure control device, for a camera, which meters the light passing through the aperture in order to generate a light metering output signal. The device also has a memory for storage of this output signal. The exposure is controlled by means of a light metering output signal in such a fashion that ideal exposure control with respect to a particular point within an object is placed in the photographic image plane.
The disadvantage of both exposure metering control systems is that the operation of the corresponding camera is made considerably more difficult, since the object elements used for the exposure metering do not necessarily lie in the image center. Thus, the object elements must first be metered and the pertinent measured values must be adopted and "stored" by pressing a button. To accomplish this requires the added fundamental switchover between "integrated" and "selective" exposure metering, which overall also complicates the design of the camera. Moreover, additional switches and displays are necessary, besides the appropriate metering buttons.